In recent years, demand for increased capacity of semiconductor devices has resulted in frequent use of stacked semiconductor devices formed by stacking a plurality of semiconductor chips on a substrate or a leadframe. For such stacked semiconductor devices, which are at the same time required to be thinner and smaller, a wire bonding method in which pads on adjacent semiconductor chips and a pad on a semiconductor chip and a lead of a leadframe are sequentially connected to each other with wire is used, instead of connecting pads on semiconductor chips in respective layers and a leadframe separately. This method uses a method in which, in order to prevent damage to semiconductor chips during wire bonding, first, a bump is formed on each pad on each semiconductor chip, then reverse bonding is performed from a lead of a leadframe onto a pad on a semiconductor chip, and further next reverse bonding is performed from the top of the bump to which bonding has been performed onto a bump on an adjacent semiconductor chip, whereby wire is sequentially connected from the leadframe to a pad on a semiconductor chip in the uppermost layer (for example, referring to Patent Literature 1).
There is proposed another method in which a bump is formed on each pad surface located on intermediate layers of a stacked semiconductor device, ball bonding is performed on a pad on a semiconductor chip in the uppermost layer, wire is looped onto a bump formed on a pad on an intermediate layer to be bonded onto the bump, then the wire is further looped onto a bump on the next semiconductor chip to be bonded, whereby the pads on adjacent intermediate layers are connected to each other with the wire (for example, referring to Patent Literature 2).